To meet the demand for wireless data traffic, which has increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Generally, in a D2D communication system, a device identifies neighbor devices which are proximate to the device itself, and transmits and receives data by establishing a radio link with a specific neighbor device if necessary. This process for establishing a radio link and transmitting and receiving data is locally performed among devices without assistance of additional apparatus, so a D2D communication system has an advantage that rapid market introduction is possible without additional infrastructure compared to other wireless communication system. Further, a D2D communication system may solve a traffic overload problem which is concentrated on a base station or an access point (AP) by locally accepting data traffic.
So, a standard organization such as a 3RD generation partnership project (3GPP), and a institute of electrical and electronics engineers (IEEE) has standardized a D2D communication standard based on long-term evolution advanced (LTE-A), wireless-fidelity (Wi-Fi), and/or the like, and various D2D communication schemes have been developed.
Recently, a 3GPP has actively progressed a standardization study for supporting a proximity service among devices. Specially, a D2D communication scheme which may increase a data rate between neighbor devices and may decrease transmission delay between the neighbor devices has been considered as a scheme which is appropriated for supporting the proximity service among the devices. Here, in order for the D2D communication scheme to effectively support the proximity service among the devices, a device needs to discover other devices which are located around the device without assistance of a base station or an AP, and identify the discovered devices.
So, a device discovery scheme in which the device informs presence of the device to neighbor devices and acquires information of the neighbor devices becomes an importance element for effectively supporting the proximity service.
Meanwhile, device discovery schemes have been variously proposed, and a discovery scheme as one device discovery scheme among the device discovery schemes will be described below.
The discovery scheme is a scheme in which devices individually transmit discovery messages which inform presence of the devices and receive discovery messages which are transmitted in other devices through a peer discovery resource (PDR) which is configured based on an orthogonal frequency division multiplexing (OFDM) scheme.
In the discovery scheme, each device considers an energy level which is detected at each PDR for individually selecting a PDR through which each device will transmit a discovery message. That is, each device randomly selects one PDR from among low L % PDRs, e.g., 5% PDRs among detected PDRs based on an energy level, and transmits a discovery message through the selected PDR thereby neighbor devices may discover the device.
If a plurality of devices are densely located at a relatively narrow area, energy levels which are detected in the plurality of devices are similar, so a case that the plurality of devices select the same PDR. If a discovery message which is transmitted in each of the plurality of devices is transmitted through the same PDR, neighbor devices may not identify the devices which transmit the discovery messages through the same PDR due to overlap of the discovery messages, and this will be described below.
Firstly, each device randomly selects one PDR among low L % PDRs based on energy levels of PDRs which are measured in each device, and transmits a discovery message through the selected one PDR. Here, if each of neighbor devices measures energy levels for PDRs one another, the energy levels for the PDRs which are measured in each of the neighbor devices becomes similar. Specially, if devices of which the number corresponds to L % of a total number of PDRs or more than L % perform a PDR selecting operation at the same time, a probability that PDRs which are duplicately selected occur becomes high even though each of the devices randomly selects one PDR among PDRs which have low L % energy level.
Here, a problem which may occur if devices which are densely located select the same PDR for transmitting a discovery message in a general D2D communication system will be described with reference to FIG. 1.
FIG. 1 schematically illustrates a problem which may occur if devices which are densely located select the same PDR for transmitting a discovery message in a general D2D communication system.
Referring to FIG. 1, in the D2D communication system, it will be assumed that two devices, i.e., a device #1 111 and a device #2 113 are adjacent each other, and energy levels for PDRs which are measured in each of the device #1 111 and the device #2 113 are similar. If a total number of PDRs which are usable in the D2D communication system is 20, the number of PDRs which have low L % energy level, e.g., low 5% energy level becomes 1.
So, each of the device #1 111 and the device #2 113 selects one PDR which has low 5% energy level, and the PDR which is selected in each of the device #1 111 and the device #2 113 may be the same since the device #1 111 and the device #2 113 are adjacent each other. In this case, since the device #1 111 and the device #2 113 select the same PDR, a discovery message which is transmitted in each of the device #1 111 and the device #2 113 is overlapped and transmitted through the same PDR. Due to this, other devices may not the device #1 111 and the device #2 113.
Meanwhile, in the discovery scheme, a specific device considers only an energy level of a related PDR without considering whether other devices use the related PDR upon selecting a PDR for transmitting a discovery message, so a problem may occur, and this will be described below.
Firstly, it will be assumed that devices which perform a D2D communication already use all PDRs which are usable in a D2D communication system. In a case that all usable PDRs are used, if a new device accesses the D2D communication system, the new device selects one PDR using the discovery scheme based on a preset peer device discovery period, and transmits a discovery message using the selected one PDR.
However, the one PDR which is selected in the new device is a PDR which is used already in a specific device. Due to this, devices which transmit a discovery message through the one PDR may not be identified. So, in the D2D communication system, the more increased the number of devices which perform a D2D communication, the more decreased the number of discovered devices is.
So, in a D2D communication system, there is a need for a PDR selecting scheme which may decrease overlap of discovery message transmission, i.e., a discovery message collision.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.